Configuration of HS-DSCH serving cell change improvements

ABSTRACT

A cell change procedure for user equipment (UE) situated in a serving cell. An active set of cells comprises a list of cells to which the UE can move from the serving cell. The UE sends a request to a network controller to add at least one further cell to the active set. The UE then receives the requested active set update from the network controller with the further cell and a list of cells to which a modified cell change procedure shall be used for handover. A neighbor cell which is stronger than a current serving cell is detected. This detected stronger neighbor cell is matching with the received list of modified cell change procedure cells, and the modified cell change procedure for the handover to the stronger neighbor cell is applied if the stronger neighbor cell is found matching a cell on the list.

TECHNICAL FIELD

The present solution relates to a method and arrangement in atelecommunications system, in particular it relates to a method andarrangement for configuring a high speed downlink shared channel(HS-DSCH) serving cell change (HSCC) procedure in a telecommunicationssystem.

BACKGROUND

A Universal Mobile Telecommunications System (UMTS) or third generation(3G) network can be separated into a number of major components, namelyone or more core networks which are responsible for setting up andcontrolling user sessions, and a UMTS radio access network (UTRAN) whichcontrols access to the air interface. The interface between UTRAN anduser equipment (UE) is provided by nodes that may be referred to as“Node B” (analogous to base stations in 2G/GSM networks) or basestations. NodeBs are responsible for transmitting and receiving dataover the air interface and are controlled by radio network controllers.User and control data is routed between a base station and a corenetwork via the base station and the radio network controllers. Theinterface between a base station and a radio network controller isreferred to as the Iub interface. The interface between two radionetwork controllers in the same network is referred to as the Iurinterface. A Iu interface carries user traffic (such as voice or data)as well as control information, and is mainly needed for soft handovers.Soft handover refers to a feature used by the Code Division MultipleAccess (CDMA) and Wideband Code Division Multiple Access (WCDMA)standards, where a user equipment, such as a cell phone, issimultaneously connected to two or more cells (or cell sectors) during acall. On the uplink (user equipment-to-cell-site), all the cell sitesectors that are actively supporting a call in soft handover send thebit stream that they receive back to the radio network controller, alongwith information about the quality of the received bits. The radionetwork controller examines the quality of all these bit streams anddynamically chooses the bit stream with the highest quality. Again, ifthe signal degrades rapidly, the chance is still good that a strongsignal will be available at one of the other cell sectors that aresupporting the call in soft handover.

In UTRAN, the high-speed downlink shared channel (HS-DSCH) does not usesoft handover as dedicated channels do. Instead, a procedure calledHS-DSCH serving cell change (HSCC) is utilized to make a hard handover.Soft handover is still used for the uplink, and an active set is managedin the same way as for non-high speed user equipment. The active setcomprises all cells the user equipment is connected to in uplink softhandover. The user equipment continuously measures the common pilot(CPICH) and comprises a hysteresis to be fulfilled during a certain time(time to trigger). The active set update procedure is schematicallyillustrated in FIG. 1. The active set update procedure is triggered bymeasurement report 1 a, 1 b or 1 c, 101 informing the radio networkcontroller 315 that new cells have fulfilled the criterions to be added(measurement report 1 a), deleted (measurement report 1 b) or replaced(measurement report 1 c) in the active set. The measurement report 1 a,1 b, 1 c is sent from the user equipment 310 to a network controller315, e.g. a serving radio network controller SRNC. A serving radionetwork controller 315 is a type of radio network controller servingparticular user equipment 310 and manages the connections towards thatuser equipment 310. When in HS-DSCH operation, the downlink is not insoft handover. Instead, one of the cells (typically the strongest) inthe active set is marked as current HS-DSCH serving cell. The networkcontroller 315 then performs a radio link addition 102, and sets up therequired radio links by sending and receiving setup request and responseto/from the base stations 350, 307. The network controller 315 transmitsthe active set update message 105 to the user equipment 310. When theuser equipment 310 has received the active set update from the networkcontroller 315, it prepares 106 a processing, i.e. it reads the messageand applies the new configuration, e.g. adds or deletes a radio link.The user equipment 310 sends an active set update complete message 107to the network controller 315 confirming that the active set update wascomplete. The duration of an active set update procedure may, as anexample, be calculated as follows:T _(asu) =Ttrig1a+2*T _(Uu)+2*T _(Iub)where

-   -   Ttrig1 a=Time to trigger measurement report 1 a=320 ms    -   Tu_(Uu)=Uu (Radio Interface) delay=100 ms    -   T_(Iub)=Iub (Radio Network Controller—NodeB Interface) delay=10        ms    -   T_(asu)=Time for active set update

The signalling sequence for a (regular) HSCC procedure for hard handoveris schematically shown in a combined flow and signalling diagram in FIG.2. The user equipment 310 performs a handover evaluation 200 todetermine whether a handover shall be performed. This is triggered by aneighbour cell (target cell) being stronger than of the current cell(serving cell). A measurement report 1 d is then sent 201 from the userequipment 310 to the network controller 315, e.g. the serving radionetwork controller (SRNC), indicating that another cell in the activeset has become the strongest one. As an example, the measurement report1 d is triggered to be sent from the user equipment when the measuredcommon pilot channel level (CPICH) of the target cell is stronger thanthe current cell by a certain hysteresis for a given time, governed by aparameter Ttrig1 d (time to trigger measurement report 1 d).

When not considering possible processing delays in the networkcontroller 315 and the user equipment 310 (i.e. in simulation), thedelay of the cell change procedure, T_(cc), used may, as an example, becalculated as follows:T _(cc) =Ttrig1d+T _(Uu)+2*T _(Iub) +T _(ActivationTime)where

-   -   T_(cc)=Delay of cell change procedure    -   Ttrig1 d=time to trigger measurement report 1 d    -   T_(Uu)=Uu (Radio Interface) delay=100 ms    -   T_(Iub)=Iub (Radio Network Controller—NodeB Interface) delay=10        ms    -   T_(ActivationTime) ⁼Activation time

When the network controller 315 receives the measurement report 1 dindicating the existence of this stronger cell, the network can take thedecision to change the serving cell, i.e. it takes a handover decision202. When a cell change is triggered, the network controller configuressource and target base stations (shown as only one base station in FIG.2) with the new configuration and configures the Iub transport bearer.The network controller 315 sends a radio link reconfiguration prepare203 message to the base stations 305, 307, and receives in return aradio link reconfiguration ready message 204. When both base stations305, 307 (serving and target) have acknowledged the configuration, thenetwork controller 315 calculates 205 the activation time for the newconfiguration in case the switch to the new configuration is asynchronized procedure, meaning that the user equipment 310 and thenetwork controller 315 i.e. serving network controller, shall move tothe new configuration at the same time. The activation time is relativeto a connection frame number (CFN). An offset is needed to cover for thetime it takes to transmit the re-configuration messages 206 to both theuser equipment 310 and the base stations 350, 307. The networkcontroller 315 sends a physical channel reconfiguration message 207 tothe user equipment 310. The user equipment 310 performs a processing206, i.e. it reads the message from the network controller 315 andapplies the new configuration, e.g. adds or deletes a radio link 208 forthe handover and sends a physical channel reconfiguration message 209 tothe network controller 315.

There is however a problem for user equipments 310 travelling at veryhigh speed, since the link quality of the source cell (i.e. servingcell) may degrade before the cell change procedure to the target cell iscompleted. If this happens before the network controller 315 is able tosuccessfully transmit the Physical Channel Reconfiguration message 209,the network controller 315 will no longer be able to reach the userequipment 310 and the call will be dropped.

Enhancements to the HS-DSCH serving cell change procedure areconsequently required regarding radio protocol procedures andstructures, Iub/Iur protocols and User equipment, base station and radioresource management (RRM) performance requirements.

Several improvements exist to the high speed serving cell changeprocedure to reduce drop rates, some of which are shortly listed below:

-   -   Transmit of the handover command in the target cell.    -   Proactive retransmissions for delay sensitive packets such as        signalling radio bearer (SRB) packets.    -   Bi-casting handover commands from both the serving Node B and        the target Node B

Any improvements and modifications, including those mentioned above, tothe regular HS-DSCH serving cell change procedures as exemplified inFIG. 2 are hereinafter referred to as modified cell change procedureswithin the context of the description of the present solution. Commonfor the above improvements is that they come at a certain cost in systemperformance. Bi-casting reduces capacity on radio and transport network,proactive retransmissions cost radio resources, and the target cellre-pointing requires resource reservation in all cells in the activeset.

SUMMARY

It is thus an object of the present solution to provide an enhancedsolution for configuring a high-speed downlink shared channel (HS-DSCH)Serving Cell Change (HSCC) procedure in a communications system.

At least one of the above objects is achieved with the methods or nodeaccording to the example aspects and embodiments of the solution hereindescribed.

Further objects and advantages are evident from the following.

The objectives set forth above are achieved by providing, in a firstaspect of the present solution, a method in a user equipment forconfiguring a cell change procedure to be used for handover in awireless communication network. The user equipment being situated in aserving cell. The user equipment comprising an active set of cells,which active set of cells comprises a list of cells to which the userequipment can move from the serving cell The method comprising thefollowing steps:

-   -   sending a request to a network controller comprised in the        wireless communication network to add at least one further cell        to the active set;    -   receiving the requested active set update from the network        controller, the active set update comprising the at least one        further cell to be added to the active set and a list of cells        to which a modified cell change procedure shall be used for        handover;    -   detecting a neighbour cell which is stronger than a current        serving cell;    -   matching the detected stronger neighbour cell with the received        list of modified cell change procedure cells; and    -   applying the modified cell change procedure for the handover to        the stronger neighbour cell if the stronger neighbour cell is        found matching a cell on the list.

In an alternative embodiment of the method according to the presentsolution the method further comprises the step of applying a regularcell change procedure for the handover if the stronger neighbour cell isfound not matching.

In another alternative embodiment of the method according to the presentsolution the modified cell change procedure comprises sending the cellchange command over the stronger neighbour cell.

In yet another alternative embodiment of the method according to thepresent solution the active set update message is transmitted via radioresource control signalling.

In still another alternative embodiment of the method according to thesolution the cells to which a modified cell change procedure is appliedis signalled by including an information element “Target cellpreconfiguration information” to the corresponding “Radio link additioninformation”.

In an alternative embodiment of the method according to the presentsolution the stronger cell is detected by a user equipment measuring ahigher signal strength in a neighbour cell compared to that of thecurrent serving cell.

In still an alternative embodiment of the method according to thesolution the measured signal is a common pilot.

In a further alternative embodiment of the method according to thepresent solution the cell change procedure is a high speed serving cellchange procedure.

In a second aspect of the present solution there is provided a method ina network controller for configuring a cell change procedure to be usedfor handover in a wireless communication network. The network controlleris arranged to be connected to a user equipment situated in a servingcell. The user equipment comprising an active set of cells, which activeset of cells comprises a list of cells to which the user equipment canmove from the serving cell. The method comprising the following steps:

-   -   receiving a request from a user equipment to add at least one        further cell to an active set; and    -   sending an active set update to the user equipment, the active        set update comprising a list of cells to be added to the active        set and a list of cells to which a modified cell change        procedure shall be used for handover.

In alternative embodiment of the method according to the second aspectof the present solution the cell change procedure is a high speedserving cell change procedure.

In a third aspect of the present solution there is provided anarrangement in a user equipment. The user equipment being comprised in awireless communication network, wherein the user equipment arrangementis arranged to configure a cell change procedure to be used for handoverin the network. The user equipment being arranged to be connected to anetwork controller. The user equipment being situated in a serving cell,and the user equipment comprising an active set of cells, which activeset of cells comprises a list of cells to which the user equipment canmove from the serving cell (306). The user equipment arrangement furthercomprises:

-   -   a sender configured to send a request to the network controller        through the an interface to add at least one further cell to an        active set;    -   a receiver configured to receive an active set update from the        network controller, the active set update comprising a list of        cells to be added to the active set and a list of cells to which        a modified cell change procedure shall be used for handover, the        lists being stored in a memory unit;    -   a detector configured to detect a neighbour cell which is        stronger than a current serving cell;    -   a processor configured to match the detected stronger neighbour        cell with the received list of modified cell change procedure        cells and to apply the modified cell change procedure for the        handover to the stronger neighbour cell (308) if the stronger        neighbour cell is found matching a cell on the list.

In an alternative embodiment of the third aspect of the present solutionthe processor is further arranged to apply a regular cell changeprocedure for the handover if the stronger neighbour cell is found notmatching.

In another alternative embodiment of the third aspect of the presentsolution the modified cell change procedure comprises sending the cellchange command over the stronger neighbour cell.

In still an alternative embodiment of the third aspect of the presentsolution the active set update message is transmitted via radio resourcecontrol signalling.

In still an alternative embodiment of the third aspect of the presentsolution the cells to which a modified cell change procedure is appliedis signalled by including an information element “Target cellpreconfiguration information” to the corresponding “Radio link additioninformation”.

In another alternative embodiment of the third aspect of the presentsolution the stronger cell is detected by a user equipment measuring ahigher signal strength in a neighbour cell compared to that of thecurrent serving cell.

In a further alternative embodiment of the third aspect of the presentsolution the measured signal is a common pilot.

In still an alternative embodiment of the third aspect of the presentsolution the cell change procedure is a high speed serving cell changeprocedure.

In a fourth aspect of the present solution there is provided anarrangement in a network controller. The network controller beingcomprised in a wireless communication network, wherein the networkcontroller is arranged to configure a cell change procedure to be usedfor handover in the wireless communication network. The networkcontroller being arranged to be connected to a user equipment situatedin a serving cell. The user equipment comprising an active set of cells,which active set of cells comprises a list of cells to which the userequipment can move from the serving cell. The network controllerarrangement further comprises

-   -   a receiver configured to receive a request from a user equipment        to add at least one further cell to an active set; and    -   a sender configured to send an active set update to the user        equipment, the active set update comprising a list of cells to        be added to the active set and a list of cells to which a        modified cell change procedure shall be used for handover.

In an alternative embodiment of the fourth aspect of the presentsolution the cell change procedure is a high speed serving cell changeprocedure.

In a fifth aspect of the present solution there is provided a computerprogram stored in a computer readable memory in a node in a wirelesscommunication network. The program being arranged to configure a cellchange procedure to be used for handover in the wireless communicationnetwork. The program comprising instruction sets for:

-   -   sending a measurement report with requests to add at least one        further cell to an active set;    -   receiving an active set update from the network controller, the        active set update comprising a list of cells to be added to the        active set and a list of cells to which a modified cell change        procedure shall be used for handover;    -   detecting a neighbour cell which is stronger than a current        serving cell;    -   matching the detected stronger neighbour cell with the received        list of modified cell change procedure cells; and for    -   applying the modified cell change procedure for the handover to        the stronger neighbour cell if the stronger neighbour cell is        found matching a cell on the list.

Since a detected stronger neighbour cell is matched with the receivedlist of modified cell change procedure cells the, the modified cellchange procedure is made configurable on a cell level. In this way, suchimprovements are used only in cells where problems with cell changeprocedure performance are monitored, and thus the cost of theimprovements in terms of system capacity may be minimized. Anotheradvantage of this is that a modified cell change procedure is adaptabledependent on target cell performance.

The features described above in relation to the method according to thesolution may, where applicable, also be implemented in an arrangementaccording to the solution with the same advantages as described inrelation to the method.

It goes without saying that the above aspects of the solution may becombined in the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The solution will now be further described in more detail in thefollowing detailed description by reference to the appended drawingsillustrating embodiments of the solution and in which:

FIG. 1 is a combined flowchart and signalling diagram illustrating aprior art active set update procedure.

FIG. 2 is a combined flowchart and signalling diagram illustrating aprior art procedure for HS-DSCH serving cell change.

FIG. 3 is a schematic block diagram illustrating a wirelesscommunication network.

FIG. 4 is a combined flowchart and signalling diagram depicting a methodfor configuring a cell change procedure to be used for handover.

FIG. 5 is a flowchart illustrating embodiments of a method in a userequipment.

FIG. 6 is a flowchart illustrating embodiments of a method in a networkcontroller.

FIG. 7 is a schematic block diagram illustrating embodiments of a userequipment arrangement.

FIG. 8 is a schematic block diagram illustrating embodiments of anetwork controller.

DETAILED DESCRIPTION

One or more embodiments herein relate to a method that allows known highspeed downlink shared channel (HS-DSCH) serving cell change (HSCC)improvements to be applied only to certain cells, e.g. cells in whichcertain performance problems have been detected. In the following, theterm cell change procedure is used for high speed downlink sharedchannel (HS-DSCH) serving cell change (HSCC) procedure. The necessaryinformation for this is transmitted to the user equipment 310 (UE)either via the active set update procedure, or via the broadcast controlchannel. Embodiments herein thus make use of cell change improvementsconfigurable on a cell level. In this way, such improvements are usedonly in cells where problems with cell change performance are monitored,and thus the cost of the improvements in terms of system capacity may beminimized. It also improves cell change reliability in difficult cells.In more detail, this description provides examples of two alternativeembodiments for configuration of whether regular or modified (i.e.special or fast) cell change procedure shall be applied by a userequipment in handover to a certain cell. In the following, the termregular cell change procedure and modified cell change procedure will beused. The particular cell change improvement that is selected is inprinciple transparent to the present solution.

The problem solved is to make the use of cell change improvementsconfigurable on a cell level. A user equipment sends a request to thenetwork to add new cells to an active set. As mentioned above, theactive set comprises all cells the user equipment is connected to inuplink soft handover. The user equipment then receives in return anactive set update comprising a list of cells to be added to the activeset and a list of cells to which a modified cell change procedure shallbe used for handover. When a user equipment detects that a cell in theactive set is stronger than the current serving cell, thus fulfillingthe criteria for event 1 d, it matches the indicated new target cellwith the received list of cells to which the modified cell changeprocedure shall be used. If the target cell is found matching on thelist, the modified cell change procedure is applied for the handover tothe target cell.

FIG. 3 shows a wireless communication network 300, using technologiessuch as e.g. UTRAN. The wireless communication network 300 comprisesbase stations serving cells, such as a base station 305 serving a cell320 and a base station 307 serving cell 308. The base stations 305 and307 are radio base stations, e.g. in a radio access network, and may bereferred to as NodeB. The base station 305 is arranged to wirelesslycommunicate with a user equipment 310 via e.g. radio frequencytransmitters and receivers which also may be responsible fortransmitting and receiving data over an air interface 312. The userequipment 310 may be referred to as a node device. The wirelesscommunication network 300 further comprises a radio network controller315 adapted to control the base stations 305, 307 and other basestations connected to it. The radio network controller 315 is the pointof contact for the user equipment 310 towards the communication network300. The network controller 315 is connected to a core network 316providing services to the user equipment 310.

The user equipment 310 moves from cell 306 towards the neighbor cell308. The user equipment 310 uses cell change procedures to move from onecell to another cell when a stronger neighbor cell is detected. When theuser equipment 310 uses HS-DSCH it uses a high speed cell changeprocedure that is modified or regular. A regular cell change procedureis as described above, and the modified cell change procedure is aprocedure that may be used only in cells where problems with HSCCperformance are monitored.

As mentioned above, several improvements, here referred to as modifiedcell change procedures exist to the high speed serving cell changeprocedure to reduce drop rates, three of which are shortly describedbelow:

Transmit the handover command in the target cell. In this improvement,the cell change command is transmitted in the target cell as opposed tothe serving cell 306 in the regular HS-DSCH serving cell changeprocedure in FIG. 2. This improves robustness in cases where the qualityof the serving cell 306 degrades before the command is transmitted.Transmitting the command in the target cell 308 that was recentlyreported as strongest cell in the active set improves the probability ofsuccessful transmission.

Proactive retransmissions for delay sensitive packets such as signallingradio bearer (SRB) packets. The RRC message including the HS-DSCHserving cell change command is transmitted on SRB. The SRB employsAcknowledged Mode RLC, i.e. RLC retransmissions are supported. Normally,retransmissions are triggered when the receiver detects a missing packetand sends a STATUS report to the transmitter, or when a poll timerexpires on the transmitter side. However, this retransmission procedureincreases delay, and in the case of a deteriorating serving cell 306,chances of successful retransmissions is reduced over time. Thus, if thetransmitter would proactively perform retransmissions of SRB packet,e.g. in consecutive TTIs, the robustness of the HS-DSCH cell changecommand would be increased. A drawback of this scheme is however thatthe resource consumption is also increased as many of the proactiveretransmissions would be unnecessary.

Bi-casting handover commands from both the serving Node B and the targetNode B. This improvement is similar to the first improvement. Here, theHS cell change command is transmitted in both source 306 and target cell308, to maximize probability of successful transmission. Compared to thefirst improvement, this should give even higher robustness to changes insource 306 and target cell 308 quality from the time the measurementreport is generated to the time the HS cell change command istransmitted.

All these improvements apply to the cell change procedures in all cellsand are here as mentioned above referred to as modified cell changeprocedures. However, the present solution applies the modified cellchange procedure only to certain cells. A modified cell change procedureapplied only to certain cells, e.g. cells in which certain performanceproblems have been detected. In this way, such improvements are usedonly in cells where problems with cell change performance are monitoredwhich improves the cell change reliability in difficult cells, and thusthe cost of the improvements in terms of system capacity is minimized.

In the cell change procedure, the user equipment 310 uses a list ofactive set of cells. The list of active set of cells comprises a list ofcells to which the user equipment 310 can move from the serving cell306.

FIG. 4 is a combined flowchart and signalling diagram depicting anexample of a method for configuring a cell change procedure to be usedfor handover. The method comprises the following steps:

Step 401

The user equipment 310 sends a request to the network controller 315 toadd a new cell, a new cell x, that may be a stronger cell to the activeset. The new cell x may e.g. be cell 308. This step may be performed inthe same way as in prior art described above.

The request may be triggered by measurements on a common pilot (CPHICH),and where the trigger comprises a hysteresis to be fulfilled over acertain time period (time to trigger).

Step 402

As a response to the request in step 401, the network controller 315sends an active set update message, e.g. of the radio resource control(RRC), to the user equipment 310. The active set update messagecomprises information about adding cell x to the list of active set ofcells stored in the user equipment 310. To improve cell changereliability in difficult cells, the active set update message furtherindicates whether the modified or the regular cell change procedureshall be used in the target cell 308. The active set update message mayin one embodiment of the present solution comprise an informationelement comprising a list of all neighbouring cells for which themodified cell change procedure shall be used. Alternatively, a newinformation element may be added for each cell in the list of addedcells, indicating whether the modified or the regular cell changeprocedure shall be used in corresponding cell. In some embodiments, thismay be signalled by including an information element “Target cellpreconfiguration information” to the corresponding “Radio link additioninformation”. The target cell preconfiguration information may alsoinclude information needed by the user equipment 310 to access thetarget cell 308. An information element is a field in a radio resourcecontrol message, carrying information.

The network controller 315 may for example use a log of dropped callsstored in the network controller 315, since a dropped call in a cellmight imply problems in that cell that would require the use of amodified cell change procedure for a hard handover to that target cell308.

Step 403

The user equipment 310 sends an active set update complete message 403to the network controller 315 confirming that the active set update wascomplete.

Step 404

When the user equipment 310 has completed the active set updateprocedure it may send, e.g. via radio resource control signalling, tothe network controller 315, a measurement report indicating the presenceof a “stronger cell”, which in this example is cell 308. The trigger tosend the report may for example be event 1 d, i.e. that the userequipment 310 has measured higher signal strength of a common pilotchannel level (CPICH) in the neighbour cell 308 comprised in the activeset of cells, than in that of the current serving cell 306. Before theuser equipment 310 transmits the measurement report 1 d, it determinesif the target cell 308 is configured for modified cell change procedureor regular cell change procedure by detecting/matching if the targetcell 308 is present on the previously received list of cells in whichmodified cell change procedure is used. The contents of the measurementreport may differ depending on whether the modified or regular cellchange procedure is to be used.

In an alternative embodiment, the information of whether modified orregular cell change procedure is applied in a particular cell isbroadcasted to user equipments 310 in a system information block (SIB)of the broadcast control channel (BCCH). As for the active set updatecase, an information element is then added containing a list ofneighbouring cells for which the modified cell change procedure shall beused in handover.

Step 405

The network controller 315 receives the measurement report, and mayperform a handover decision based on the received measurement report.

Step 406

The network controller 315 may then configure the serving base station305 and the target base station 307 with the new configuration, andconfigures the Iub transport bearer. The network controller 315 mayperform this by sending a radio link reconfiguration prepare message toboth serving 305 and target base station 307.

Step 407

The network controller 315 may receive in return a radio linkreconfiguration ready message from the serving base station 305 and thetarget base station 307.

Step 408

When the serving base station 305 and target base station 307 haveacknowledged the configuration by sending the reconfiguration readymessage, the network controller 315 may calculate the activation time(e.g. T_(asu)) for the new configuration in case the switch to the newconfiguration is a synchronized procedure, meaning that the userequipment 310 and the network controller 315 shall move to the newconfiguration at the same time. The activation time is relative to aconnection frame number (CFN). In the case of unsynchronized procedure,no activation time is used.

Step 409

The network controller 315 may send a radio link reconfiguration committo the serving and target base stations 305, 307.

Step 410

The network controller 315 may send a physical channel reconfigurationmessage to the user equipment 310. The message indicates to the userequipment 310 that it shall be configured to the stronger neighbour cell308.

Step 411

In case the modified cell change procedure is used, the target basestation 307 may also schedule the user equipment 310 on the HS-SCCH,thus indicating to the user equipment 310 that the preconfigured cellchange is approved by the network controller 315. In this way, thereliability of the cell change procedure is improved in case the sourcecell signal level has deteriorated, e.g. for fast moving userequipments, or due to street corner effects, or similar.

Step 412

The user equipment 310 prepares a processing, i.e. it reads thereconfiguration message from the network controller 315 or thepre-configuration information in case it received the target cellHS-SCCH order.

Step 413

The user equipment 310 then executes the handover. If the synchronizedprocedure is used the handover execution is performed at the calculatedactivation time.

Step 414

The user equipment 310 may send a physical channel reconfigurationcomplete message to the network controller 315 after the handover hasbeen completed.

The method described above will now be described seen from theperspective of the user equipment 310. FIG. 5 is a flowchart describingthe present method in the user equipment 310 for configuring a cellchange procedure to be used for handover in a wireless communicationnetwork 300. As mentioned above, the user equipment 310 is situated inthe serving cell 306. The user equipment 310 comprises a list of activeset of cells, the list of active set of cells comprises a list of cellsto which the user equipment 310 can move from the serving cell 306. Themethod comprises the further steps to be performed by the user equipment310:

Step 501

The user equipment 310 sends a request to the network controller 315comprised in the wireless communication network 300, to add at least onefurther cell to the active set.

Step 502

The user equipment 310 receives the requested active set update from thenetwork controller 315. The active set update comprises the list of atleast one further cell to be added to the active set and a list of cellsto which a modified cell change procedure shall be used for handover.

In some embodiments the active set update message may be transmitted viaradio resource control signalling.

In some embodiments, the cell change procedure is a high speed servingcell change procedure.

Step 503

The user equipment 310 detects a neighbour cell 308 which is strongerthan a current serving cell 306.

According to some embodiments the stronger cell 308 may be detected by auser equipment 310 measuring a higher signal strength in a neighbourcell 308 compared to that of the current serving cell 306.

In some embodiments the measured signal may be a common pilot.

Step 504

The user equipment then 310 matches the detected stronger neighbour cell308 with the received list of modified cell change procedure cells.

Step 505

The user equipment 310 applies the modified cell change procedure forthe handover to the stronger neighbour cell 308 if the strongerneighbour cell 308 is found matching a cell on the list.

Step 506

This is an optional step. In some embodiments the user equipment 310 mayapply a regular cell change procedure for the handover if the strongerneighbour cell 308 is found not matching.

In some embodiments the modified cell change procedure may comprisesending the cell change command over the stronger neighbour cell 308.

In some embodiments, the cells to which a modified cell change procedureis applied may be signalled by including an information element “Targetcell preconfiguration information” to the corresponding “Radio linkaddition information”.

The method described above will now be described seen from theperspective of the network controller 315. FIG. 6 is a flowchartdescribing the present method in the network controller 315 forconfiguring a cell change procedure to be used for handover in awireless communication network 300. The network controller 315 isconnected to a user equipment 310 situated in a serving cell 306. Theuser equipment 310 comprises an active set of cells, which active set ofcells comprises a list of cells to which the user equipment 310 can movefrom the serving cell 306. The method comprises the further steps to beperformed by the network controller 315:

Step 601

The network controller 315 receives a request from a user equipment 315to add at least one new cell to an active set.

Step 602

The network controller 315 sends an active set update to the userequipment 315. The active set update comprises list of cells to be addedto the active set and a list of cells to which a modified cell changeprocedure shall be used for handover.

To perform the method steps shown in FIG. 5 for configuring a cellchange procedure to be used for handover in a wireless communicationnetwork 300 the user equipment 310 comprises a user equipmentarrangement 700 as shown in FIG. 7. The user equipment 310 is arrangedto be connected to a network controller 315, and the user equipment 310is situated in a serving cell 306. The user equipment 310 comprises anactive set of cells stored in a memory 710, which active set of cellscomprises a list of cells to which the user equipment 310 can move fromthe serving cell 306.

The user equipment arrangement 700 comprises a sender 720 configured tosend a request to the network controller 315 through an interface 312 toadd at least one further cell to an active set. The user equipmentarrangement 700 also comprises a receiver 730 configured to receive anactive set update from the network controller 315, the active set updatecomprising a list of cells to be added to the active set and a list ofcells to which a modified cell change procedure shall be used forhandover, the lists being stored in the memory unit 710. It alsocomprises a detector 740 configured to detect a neighbour cell 308 whichis stronger than a current serving cell 306, and a processor 750configured to match the detected stronger neighbour cell 308 with thereceived list of modified cell change procedure cells and to apply themodified cell change procedure for the handover to the strongerneighbour cell 308 if the stronger neighbour cell is found matching acell on the list.

To perform the method steps shown in FIG. 6 for configuring a cellchange procedure to be used for handover in a wireless communicationnetwork 300 the network controller 315 comprises a network controllerarrangement 800 as shown in FIG. 8. The network controller 315 isarranged to configure a cell change procedure to be used for handover inthe wireless communication network 300, and the network controller 315is arranged to be connected to a user equipment 310 situated in aserving cell 306. The user equipment 310 comprising an active set ofcells, which active set of cells comprises a list of cells to which theuser equipment 310 can move from the serving cell 306.

The network controller arrangement 800 comprises a receiver 810configured to receive 601 a request from a user equipment 315 to add atleast one further cell to an active set; and a sender 820 configured tosend 602 an active set update to the user equipment 315, the active setupdate comprising a list of cells to be added to the active set and alist of cells to which a modified cell change procedure shall be usedfor handover.

The present mechanism for configuring a cell change procedure to be usedfor handover in a wireless communication network may be implementedthrough one or more processors, such as a processor 750 depicted in FIG.7, together with computer program code for performing the functions ofthe present solution. The program code comprises instruction sets for:

-   -   sending a measurement report with requests to add at least one        further cell to an active set;    -   receiving an active set update from the network controller 315,        the active set update comprising a list of cells to be added to        the active set and a list of cells to which a modified cell        change procedure shall be used for handover;    -   detecting a neighbour cell 308 which is stronger than a current        serving cell 306;    -   matching the detected stronger neighbour cell 308 with the        received list of modified cell change procedure cells; and for    -   applying the modified cell change procedure for the handover to        the stronger neighbour cell 308 if the stronger neighbour cell        308 is found matching a cell on the list.

The program code mentioned above may also be provided as a computerprogram product, for instance in the form of a data carrier carryingcomputer program code for performing the present solution when beingloaded into the user equipment 310. One such carrier may be in the formof a CD ROM disc. It is however feasible with other data carriers suchas a memory stick. The computer program code can furthermore be providedas pure program code on a server and downloaded to the user equipment310 remotely.

An advantage with the preferred embodiments of the present solution isthat cell change improvements can be applied with minimum impact onsystem capacity.

Means mentioned in the present description can be software means,hardware means or a combination of both.

The described subject matter is of course not limited to the abovedescribed embodiments, but can be modified within the scope of thegeneral concept of the solution.

The invention claimed is:
 1. A method in a user equipment forconfiguring a cell change procedure to be used for handover in awireless communication network, the user equipment being situated in aserving cell and utilizing a list of cells belonging to an active set,said list including cells to which the user equipment can move from theserving cell, the method comprising: sending a measurement report to anetwork controller in the wireless communication network that informsthe network controller to add at least one further cell to the activeset; receiving, responsive to said measurement report, an active setupdate from the network controller, the active set update comprisinginformation about the at least one further cell to be added to theactive set and an information element indicating whether the at leastone further cell is to be added to a list of cells for which a modifiedcell change procedure shall be used for hand over; detecting a neighborcell which is stronger than the serving cell; determining whether theneighbor cell matches a cell in the list of cells for which the modifiedcell change procedure shall be used; and applying the modified cellchange procedure for handover to the neighbor cell if the neighbor cellmatches a cell on that list.
 2. A method according to claim 1, whereinthe method further comprises applying a regular cell change procedurefor the handover if the neighbor cell does not match a cell on said listof cells for which a modified cell change procedure shall be used.
 3. Amethod according to claim 1, wherein the modified cell change procedurecomprises sending a cell change command over the neighbor cell.
 4. Amethod according to claim 1, wherein the active set update message istransmitted via radio resource control signaling.
 5. A method accordingto claim 1, wherein the cells to which a modified cell change procedureis applied is signaled by including an information element “Target cellpreconfiguration information” to the corresponding “Radio link additioninformation”.
 6. A method according to claim 1, wherein detecting aneighbor cell which is stronger than the serving cell comprisesmeasuring a higher signal strength in the neighbor cell compared to thatof the current serving cell.
 7. A method according to claim 6, where themeasured signal is a common pilot.
 8. A method according to claim 1,wherein the cell change procedure is a high speed serving cell changeprocedure.
 9. A method in a network controller for configuring a cellchange procedure to be used for handover in a wireless communicationnetwork, the network controller arranged to be connected to a userequipment situated in a serving cell, and the user equipment utilizing alist of cells belonging to an active set, said list including cells towhich the user equipment can move from the serving cell, the methodcomprising: receiving a measurement report from a user equipmentinforming the network controller to add at least one further cell to anactive set; and sending an active set update to the user equipment, theactive set update comprising information about the at least one furthercell to be added to the active set and an information element indicatingwhether the at least one further cell is to be added to a list of cellsfor which a modified cell change procedure shall be used for handover.10. A method according to claim 9, wherein the cell change procedure isa high speed serving cell change procedure.
 11. A user equipment in awireless communication network adapted to configure a cell changeprocedure to be used for handover in the network, the user equipmentutilizing a list of cells belonging to an active set, said listincluding cells to which the user equipment can move from the servingcell, the user equipment comprising: a sender configured to send ameasurement report to a network controller through an interfaceinforming the network controller to add at least one further cell to theactive set; a receiver configured to receive an active set update fromthe network controller, the active set update comprising informationabout the at least one further cell to be added to the active set and aninformation element indicating whether the at least one further cell isto be added to a list of cells for which a modified cell changeprocedure shall be used for handover; a detector configured to detect aneighbor cell which is stronger than a serving cell in which the userequipment is situated; and a processor configured to determine whetherthe neighbor cell matches a cell in the list of cells for which themodified cell change procedure shall be used, and to apply the modifiedcell change procedure for handover to the neighbor cell if the neighborcell matches a cell on that list.
 12. A user equipment according toclaim 11, wherein the processor is further configured to apply a regularcell change procedure for the handover if the neighbor cell does notmatch a cell on said list of cells for which a modified cell changeprocedure shall be used.
 13. A user equipment according to claim 11,wherein the modified cell change procedure comprises sending a cellchange command over the neighbor cell.
 14. A user equipment according toclaim 11, wherein the active set update message is transmitted via radioresource control signaling.
 15. A user equipment according to claim 11,wherein the cells to which a modified cell change procedure is appliedis signaled by including an information element “Target cellpreconfiguration information” to the corresponding “Radio link additioninformation”.
 16. A user equipment according to claim 11, wherein thedetector is configured to detect a neighbor cell which is stronger thanthe serving cell by measuring a higher signal strength in the neighborcell compared to that of the serving cell.
 17. A user equipmentaccording to claim 16, where the measured signal is a common pilot. 18.A user equipment according to claim 11, wherein the cell changeprocedure is a high speed serving cell change procedure.
 19. A networkcontroller in a wireless communication network adapted to configure acell change procedure to be used for handover in the network, thenetwork controller also adapted to connect to a user equipment situatedin a serving cell, the user equipment utilizing a list of cellsbelonging to an active set, said list including cells to which the userequipment can move from the serving cell, the network controllercomprising a receiver configured to receive a measurement report fromthe user equipment informing the network controller to add at least onefurther cell to an active set; and a sender configured to send an activeset update to the user equipment, the active set update comprisinginformation about the at least one further cell to be added to theactive set and an information element indicating whether the at leastone further cell is to be added to a list of cells for which a modifiedcell change procedure shall be used for handover.
 20. The networkcontroller according to claim 19, wherein the cell change procedure is ahigh speed serving cell change procedure.
 21. A computer program productstored in a non-transitory computer-readable memory and comprising astored computer program for use in a node in a wireless communicationnetwork, the program being arranged to configure a cell change procedureto be used for handover in the wireless communication network, theprogram comprising instruction sets for: sending a measurement reportthat informs a network controller in the network to add at least onefurther cell to an active set; receiving an active set update from thenetwork controller, the active set update comprising information aboutthe at least one further cell to be added to the active set and aninformation element indicating whether the at least one further cell isto be added to a list of cells for which a modified cell changeprocedure shall be used for handover; detecting a neighbor cell which isstronger than a serving cell in which the node is situated; determiningwhether the neighbor cell matches a cell in the list of cells for whicha modified cell change procedure shall be used; and for applying themodified cell change procedure for hand over to the neighbor cell if theneighbor cell matches a cell on that list.